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Dekatronic

(6″ x 8″, wood, glass, obsolete electronics)Responding to the personal pace of the viewer, this piece employs Soviet era technology imported from Russia to count down to cold war nuclear destruction.

This is an art piece I made as part of a series that all fit inside small wooden boxes that mount on the wall. They have a slightly steampunk look and are built using outdated technology. This piece contains two vintage dekatron counting tubes which are viewed in an angled mirror. They form tens and units of a counter: when the neon glow spot on one dekatron moves round a full turn, it kicks the next one on one place. Also the speed of the counting is light dependent, so if you put your hand in front of the art it slows down.

The counting trigger is derived from a neon relaxation oscillator which pulses regularly with an orange flash. The circuit also features a gas-filled voltage regulator which makes for a cool-looking central silver tube, and actually glows purple, although its not really possible to see this.

This piece has much in common with my 867-5309 piece and makes use of some very high voltages inside to make the dekatrons function, deriving around 450V from the mains input.

I do like the technical aspects of thinking up and building this kind of strange art. Below you can find the circuit schematic. For interested people, I will now describe how this machine functions with a technical walkthrough.

The circuit is a lot simpler than my 867-5309 work. It uses some of the same basic building blocks. The counting pulses are derived from a neon relaxation oscillator which is at the top right of the diagram. This one has a light dependent resistor which increases the charging current of the oscillator when more light is present in the room. This makes the 22nF capacitor charge more rapidly towards the neon strike voltage. If the room is too dark, the oscillator stops altogether. There is a booster stage to make a strong negative 150V pulse that I have described in the 867-5309 write-up and so won’t repeat here.

This art piece uses different dekatrons than the other one. These OG4 dekatrons are designed for divide by 10 counting. They have one anode and four cathodes. Two of the cathodes are for moving the glow discharge along during the application of a quadrature voltage pulse. One cathode is common for nine of the digits and the last one is for the zero, or carry digit, and is used to extract a signal when the cycle completes.

A pulse forming network is used to convert the 150V negative going clock pulse into a quadrature voltage pulse. This network requires a +36V bias voltage. I used the pulse forming network from the datasheet, but the documentation is in Russian, so I just had to decrypt it, knowing a bit of Cyrillic and guessing at things.

A high voltage transistor is used to generate the carry pulse to increment the second counter, and this transistor is turned on by the cathode current when the neon glow of the first dekatron moves to the 12 o’clock position.

The rest of the circuit is the power supply. A transformer is used to step up the mains to around 250V peak. A half wave rectifier and filter capacitor gives the main DC supply and this is stabilized with an OA2 gas filled voltage regulator tube to give +150V, which is also divided down to give 36V. I could have used a 150V zener here but the tube was prettier.

The +450V high tension comes from a voltage doubler. It is more robust than the one in the 867-5309 art piece, since these dekatrons take a slightly higher anode voltage and there are two of them. Electrolytic capacitors are used and there is a diode to prevent reverse charging of the pump capacitor.